1. Field of the Invention
The present invention relates to a combination of a tool holder defining a substantially cylindrical bore, and a tool shaft releasably received in said bore.
The invention also relates to a tool holder and a tool shaft for use in such combination.
2. Description of Prior Art
U.S. Pat. No. 1,844,446 and German Utility Model Specification No. 7,439,278 disclose a tool holder having a socket member with a cylindrical, axial bore adapted to receive a tool shaft therein. A driving element is mounted displaceably in the socket member so as to be movable between an extended position in which part of the driving member extends into the cylindrical bore, and a retracted position in which the driving member is retracted from the cylindrical bore, and the driving element is biased towards its extended position by spring means. When the tool shaft is inserted into the cylindrical bore of the socket member the driving element is pushed to its retracted position, and when the tool shaft has been fully inserted into the cylindrical bore the spring biased driving element may move to its extended position in which it is partly received in a recess formed in one side of the tool shaft, whereby the driving element prevents the tool shaft from being moved axially out from the cylindrical bore of the socket member and renders it possible to transmit rotational forces from the tool holder to the tool shaft received therein. The said known tool holders and the corresponding tool shafts are adapted so that rotational movement of the tool shaft in the direction opposite to the normal rotational direction of the associated tool causes the driving element of the tool holder to be moved out of engagement with the recess in the tool shaft due to camming action, whereby the tool shaft is released and may be removed from the tool holder.
When in use a tool mounted in a tool holder of the above described known type may be subjected to an axial force directed away from the holder, and it may happen that at the same moment the tool and consequently also the tool shaft are subjected to a torque which is very small or may even be directed opposite to the normal rotational direction of the tool. Under such circumstances it may happen that the tool shaft is inadvertently released from the tool holder. Even though the risk of such inadvertent release is present in connection with almost any type of rotational tools it is especially pronounced in connection with rotating tools of the percussive type, such as hammer drills.